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Allergies Health Center

Drug Allergies

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Many drugs can cause adverse side effects, and certain medicines can trigger allergic reactions. In an allergic reaction, the immune system mistakenly responds to a drug by creating an immune response against it. The immune system recognizes the drug as a foreign substance and the body produces certain chemicals, such as large amounts of histamine, in an attempt to expel the drug from the body.

What Are the Symptoms of a Drug Allergy?

Symptoms of a drug allergy can range from mild to life-threatening. Even in people who aren't allergic, many drugs can cause intolerance and irritation, such as an upset stomach. But during an allergic reaction, the release of histamine can cause symptoms like hives, skin rash, itchy skin or eyes, congestion, and swelling in the mouth and throat.

A more severe reaction, called anaphylaxis, may include difficulty breathing, blueness of the skin, dizziness, fainting, anxiety, confusion, rapid pulse, nausea, diarrhea, and abdominal problems.

What Are the Most Common Drug Allergies?

Historically, the drug most people are allergic to is penicillin. Other antibiotics similar to penicillin can also trigger allergies.

Other drugs commonly found to cause allergic reactions include sulfa drugs, barbiturates, anticonvulsants, and insulin.

How Are Drug Allergies Diagnosed?

A doctor diagnoses drug allergies by carefully reviewing your medical history and symptoms. If your doctor suspects that you are allergic to an antibiotic, such as penicillin, he or she may do a skin test to confirm it. However, skin testing does not work for all drugs, and in some cases it could be dangerous. If you have had a severe, life-threatening reaction to a particular drug, your doctor will simply rule out that drug as a treatment option for you. Conducting an allergy test to determine if the initial reaction was a "true" allergic response isn't worth the risk, especially if there are other drug options.

How Are Drug Allergies Treated?

The primary goal when treating an allergic drug reaction is symptom relief. Symptoms such as rash, hives, and itching can often be controlled with antihistamines, and occasionally corticosteroids.

For coughing and lung congestion, drugs called bronchodilators may be prescribed to widen the airways. For more serious anaphylactic symptoms -- life-threatening allergic reactions including difficulty breathing or loss of consciousness -- epinephrine may be given.

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